1. Field of the Invention
This invention relates to optical devices and more particularly to an improved apparatus and method for the fabrication of optical devices and electro-optical devices within a wide-bandgap semiconductor substrate by directing a thermal energy beam onto the wide-bandgap semiconductor substrate.
2. Description of the Related Art
Conventional semiconductors such as silicon have been used for various electrical, electronic and electro-optical devices. Conventional semiconductors are limited to operating temperatures below 250° C., due to the narrow band gap and poor thermal stability. There has been an increasing need to extend the limits of sensors for high temperature and harsh environments operations.
Wide-bandgap semiconductors have many advantages over conventional semiconductors such as silicon. One wide-bandgap semiconductor suitable for replacing conventional silicon-based devices is silicon carbide (SiC). The bandgap of 6H—SiC silicon carbide (SiC) is around 3 eV [2] which is about two times greater than the bandgap of silicon. Furthermore, silicon carbide (SiC) supports very high breakdown field, 3-5 MV/cm. The high sublimation temperature about 2700° C. and extremely low intrinsic carrier concentration allows silicon carbide (SiC) to operate at elevated temperatures. The dependence of intrinsic carrier concentration on temperature causes threshold voltage-shift and leakage current, resulting in device degradation and latchup phenomenon. The strong covalent bonds between Si and C yield high frequency lattice vibrations, generating high energy optical phonons (100-120 meV), that lead to a high saturation drift velocity (2×10′ cm/s) and excellent thermal conductivity (490 W/m·K).
Silicon carbide (SiC) is the only wide bandgap semiconductor that has silicon dioxide as its native oxide analogous to silicon. Silicon carbide (SiC) is potentially superior to other compound semiconductors since silicon carbide (SiC), allows the creation of a metal oxide.
Silicon carbide (SiC) is a promising semiconductor material for optical devices, particularly mirrors and lenses because of its low thermal coefficient of expansion, hardness (and hence good polishability), high thermal conductivity (350-490 Wm−1K−1) and chemical stability in hostile environments.
Doping is a challenge for silicon carbide (SiC) due to the hardness, chemical inertness and the low diffusion coefficient of most impurities of silicon carbide (SiC). Current doping techniques for silicon carbide (SiC) device fabrication include epilayer doping and ion implantation.
Epilayer doping is introduced during chemical vapor deposition (CVD) epitaxial growth. Nitrogen (N) or phosphorous (P) are used as a doping material for n-type silicon carbide (SiC) whereas aluminum (Al) and boron (B) are used as a doping material for p-type silicon carbide (SiC). Vanadium (V) is used as a doping material for semi-insulating silicon carbide (SiC).
Ion implantation is the most common doping technique used for silicon carbide (SiC). However, ion implantation generates implantation-induced defect centers in the silicon carbide (SiC) and therefore, high annealing temperatures are required to remove this damage and to electrically activate the dopants. Some defects remain in silicon carbide (SiC) for up to 1700° C. annealing temperatures. Annealing at these high temperatures can cause severe surface damage due to silicon (Si) sublimation and redistribution.
A laser conversion technology for wide bandgap semiconductors including silicon carbide (SiC) is disclosed in the prior inventions of Nathaniel R. Quick. Discussion of wide bandgap materials and the processing thereof are set forth in U.S. Pat. No. 5,145,741; U.S. Pat. No. 5,391,841; U.S. Pat. No. 5,793,042; U.S. Pat. No. 5,837,607; U.S. Pat. No. 6,025,609; U.S. Pat. No. 6,054,375; U.S. Pat. No. 6,271,576 and U.S. Pat. No. 6,670,693 are hereby incorporated by reference into the present application.
The above prior inventions of Nathaniel R. Quick disclose the fabrication of various electrical and electronic devices. The present invention expands the prior inventions of Nathaniel R. Quick by fabricating optical devices and electro-optical devices in a wide bandgap semiconductor through a laser conversion process.
Therefore, it is an object of the present invention to provide optical devices and electro-optical devices and a method of making through a laser conversion process of a wide bandgap semiconductor.
It is an object of the present invention to provide an optical device and method of making by directing a thermal energy beam onto a selected portion of the wide-bandgap semiconductor substrate for changing an optical property of the selected portion to form the optical device.
Another object of the present invention is to provide an optical device and method of making an optical device on the surface of a wide-bandgap semiconductor substrate or within a wide-bandgap semiconductor substrate.
Another object of the present invention is to provide an optical device and method of making an optical device for defining a shape of the optical device in the wide-bandgap semiconductor substrate.
Another object of the present invention is to provide an optical device and method of making an optical device including the formation of electrodes on a wide bandgap semiconductor adjacent to the optical device for forming an electro-optical device.
The foregoing has outlined some of the more pertinent objects of the present invention. These objects should be construed as being merely illustrative of some of the more prominent features and applications of the invention. Many other beneficial results can be obtained by modifying the invention within the scope of the invention. Accordingly other objects in a full understanding of the invention may be had by referring to the summary of the invention, the detailed description describing the preferred embodiment in addition to the scope of the invention defined by the claims taken in conjunction with the accompanying drawings.